You should also consider whether it is one of the old Italian 'limonimedica' varieties.
There are many of these lemon X citron hybrids in Italy and it is difficult to tell them apart from a distance.
There is one becoming increasingly popular called 'Maxima'. (This is the variety name and not connected with C. grandis = C. maxima = pummelo).
C. limonimedica 'Maxima' produces large fruit which look rather like yours. There are many photos online. The skin and pith layer is usually thinner than yours, but thicker peel is often a feature of citrus fruits grown in cooler conditions.
No idea about the 'Ibero' name, except that it suggests a connection with Spain.
